This invention relates to a tumble valve arrangement for an engine, and more particularly to an improved tumble valve arrangement for an engine of the type having only a single intake valve for each of its combustion chambers.
The design of the induction system, like many other features in an internal combustion engine, represents a compromise of the optimum design for a given engine running and load condition. That is, where an engine is designed to operate over a wide variety of engine running conditions, certain components, such as the induction system, are designed to compromise the performance under certain conditions to try to improve the performance as much as possible throughout the entire engine speed and load ranges.
For example, an induction system that is efficient at low and mid-range speeds will provide too much restriction to the air flow under high-speed performance, and high-speed performance will deteriorate. That is, under low speed and low loads it is desirable to have the charge enter the combustion chamber at a relatively high velocity and also so as to generate turbulence in the combustion chamber. Under low speed, low load conditions, the turbulence is desirable as it improves flame propagation and will ensure complete combustion. On the other hand, a turbulence-inducing induction system will restrict the flow at high speeds and high loads, and hence can deteriorate high-speed performance.
Conventional induction systems, therefore, represent a compromise between optimum low speed and optimum high speed performance. The actual type of performance which is preferred will depend upon the application for the engine.
There has been proposed, however, induction systems that employ various devices wherein the induction system can have a wider range of performance improvement. For example, the use of control valves in the induction passage to alter its shape and/or effective cross-sectional area may be employed so as to permit performance increases across the entire engine speed and load ranges.
One type of turbulence-generating system and control valve which has been employed includes a control valve which directs the flow of the intake charge through the intake port in different directions depending upon the engine running condition. Under high-speed conditions, the control valve provides substantially no restriction to the intake charge, and the intake charge is delivered generally in an axial direction into the combustion chamber.
Under low speed, low load conditions, however, the intake charge is directed to flow primarily into the cylinder through one side of the intake port and generate a tumble action within the combustion chamber. Tumble is a type of swirl, but it occurs about an axis that extends transversely to the axis of the cylinder bore rather than around it. It has been found that tumble has a number of advantages. Specifically, the tumble action tends to become accelerated as the piston approaches top dead center, and thus may provide more efficient turbulence under low speed, low load conditions.
Normally these tumble control valves have been employed in engines having plural intake valves per cylinder. However, the advantages can also be employed in conjunction with engines having only a single intake valve per cylinder.
It is, therefore, a principal object of this invention to provide an improved induction system and tumble arrangement for an engine having only a single intake valve per cylinder.
It is a further object of this invention to provide an improved arrangement for introducing turbulence to an engine having only a single intake valve per cylinder wherein the induction passage and control valve are configured and arranged so as to provide the desired degree of motion in the combustion chamber when the control valve is in its turbulence-generating position.
There is a further advantage to the use of tumble, as opposed to swirl, as a turbulence-generating media. In some instances it is desirable to attempt to stratify the charge in the combustion chamber. By employing a stratified charge, the entire charge within the combustion chamber need not be stoichiometric in order for combustion to be initiated. However, where such a lean total charge is employed in the combustion chamber, it is necessary to ensure that a stoichiometric charge is present at the gap of the spark plug at the time it is fired.
With swirl, it may be difficult to ensure that the stoichiometric charge is kept present at the spark gap at the time of spark firing unless precombustion or torch chambers are employed. With tumble, on the other hand, it is possible to provide a rich fuel-air mixture on one side of a plane containing the cylinder bore axis and on which the spark plug lies while the other side of the plane may be substantially leaner. Since the tumble motion occurs about an axis transverse to the cylinder bore axis, the tumble action will not cause the same degree of mixing in the combustion chamber as occurs with swirl.
It is, therefore, a still further object of this invention to provide an improved tumble arrangement for an internal combustion engine wherein the stratified charge may be obtained and maintained.
It is a further object of this invention to provide an improved induction system arrangement for an internal combustion engine using only a single intake valve wherein a stratified charge may be obtained and maintained throughout the stroke of the piston and around the spark gap at the time of firing.